Building a game demo with Claude Code in one day

#claude #ai #gamedev #godot

On a Sunday afternoon I pulled in a game template. That was 1:46 PM. The next time I looked up it was 3 AM, and the last commit message read "trial (demo)". There were 86 commits in between.

The result is Reptile Catcher. You go out to catch lizards by stunning them, sell them, and breed them for prettier patterns. It runs on Godot, and Claude Code wrote the code. My part was setting the direction, playtesting, and picking the assets.

A working loop in five minutes

Five minutes after the template went in, the catch-sell-breed loop was running. Honestly, I expected that much. AI can do that these days.

What mattered was the next minute. The very next commit was a balance simulator where a bot plays the game for you.

Incremental games are a numbers game. Change one upgrade price and a 30-minute stretch can turn into three hours. I can't replay the whole thing from the start every time. So every time Claude changed a number, it ran the bot, and I made calls based on numbers like "4h 19m to the ending (bot)". Later we split the bot into five personalities: one that buys attack first, one that buys the cheapest thing, one that only breeds, and so on.

The bot also caught a bug. While measuring the demo length, one bot never finished. It turned out it was stuck trying to buy an upgrade that was locked in the demo. The bug was on the bot side, but it showed me the lock rules were scattered across the code.

Changing direction at 2:20 PM

The first 30 minutes produced a screen of tabs and buttons. At 2:20 PM I changed direction completely: pixel art, catching as a "run" where you move a character yourself, and upgrades as a tree that branches out like a mind map.

Normally, throwing things out at that point would scare me. But rebuilding was so cheap that I barely hesitated. That's the biggest difference I've felt working with AI.

AI generates the sprites, I pick

The pixel sprites came from PixelLab, connected to Claude through MCP. Claude generated a few candidates, and I picked one with notes like "number 3, but make the neck shorter." Claude recorded the seed of each picked sprite in a doc.

The funny part is why some species got replaced.

The house gecko looked like every other species once it was shrunk to a 32-pixel side view, so I changed it to a skink.
The flying lizard's wing membrane didn't show up at 32 pixels, so I changed it to a frilled lizard.
The bearded dragon's walk cycle looked like a puppy no matter what, so I replaced it with a horned lizard.

Instead of regenerating until I got the sprite I wanted, I changed the game to fit what the tool draws well. For a small game, that was much faster.

My job was removing what the AI built

Around 7 PM I removed a whole set of features Claude had built that afternoon: auto-catching, auto-selling, and offline progress. Ten minutes later, prestige and the fame tree went too.

I had decided this game would be "no failing, no prestige, one straight run that ends in 4 to 6 hours." Idle features and prestige had no place in that. With the AI building this fast, features pile up quickly, but deciding what to cut was still up to me. Looking back, that was most of my work on day one.

Still, a week to ship

By 3 AM the demo scope was cut, but the actual release was October 11. In between, Claude added four bosses, drew the area backgrounds, fixed the demo lock bugs, and prepared the screenshots, cover, and web build for the itch.io page.

So "made in a day" is only true up to the demo. Building took a day, but polishing and shipping took a week. I suspect the next game will go the same way.

If you're building a numbers-heavy game with AI and don't have a simulator yet, I'd suggest having the AI build a bot right after the core loop. For me, that was the best decision of the whole project.

The demo is on itch.io. Come catch some lizards 🦎
👉 https://krenin.itch.io/reptile-catcher